This invention relates to a data processor used in a videotex or teletext system and, particularly to improvement of hardware of a character data processor.
Recently a microcomputer-implemented character data processor for a teletext system has been introduced into TV receivers. In such TV receivers, it is necessary to store character data from a broadcasting station in a data memory and also to read out the stored data for character display.
In a teletext system, in order to enhance data transmission efficiency, various data compression schemes have been developed. A typical one of these schemes is a "run length coding" scheme in which the successive number of the same information ("1" or "0") is coded as run length data. Compressed character data pattern packets of the teletext system are transmitted from a broadcasting station according to the run length scheme. The broadcasting station also transmits plural units of color data representing the character data. Each unit of the color data is formed of color information and run length information of the color.
When such compressed character data is received, a teletext TV receiver repeatedly writes in a memory the same information ("1" or "0") of character data for a number designated by the run length data. A conventional approach to perform such repetitive writing is based on software. More specifically, every time when the character data is transferred to the memory, the CPU of the microcomputer checks, according to the content of an index counter, etc., whether or not the repetitive times that the same information has been written ("1" or "0") has reached the number being designated by the run length data. If this repetition has not yet reached the designated number, the succeeding same information ("1" or "0") is transferred to the next address of the memory, and the new repetitive times of the same information are compared with the designated number. Unless the repetition has reached the designated number, the CPU is restricted to performing the routine of the above repetitive writing and cannot perform the next routine. From this, the total time for handling the compressed character data tends to become long, and overall processing for a teletext character data requires a relatively long time.